Molding powder containing organosiloxane resin and ethanolamine



Patented Nov. 7, l950 MOLDING POWDER CONTAINING ORGANO- SILOXANE RESINAND ETHANOLAMINE William W. Pedersen, Cleveland Heights, Ohio, assignorto Dow Corning Corporation, Midland, Mich., a corporation of Michigan NoDrawing. Application April 16, 1946, Serial No. 662,606

1 The present invention relates to methods of molding in which moldingpowders are employed, and to the novel molding powders, per se.

In general, molding powders which are known in the art produce moldedarticles which do not have substantial thermal stability, inasmuch asthey are based upon organic resins. This is true even of thethermosetting phenol formaldehyde type of resin.

Objects of the present invention are to provide novel molding powdersand methods of molding such powders which provide molded pieces ofimproved thermal stability.

The molding powders of the present invention comprise an inorganicfiller impregnated with an organosiloxane resin and an ethanolamine. Theorganosiloxane resin in the molding powder is preferably in a partiallycured state. The molding powders hereof are molded under pressure eitherat room temperature or at elevated temperature. Following molding theymay be cured, if desired, by heating as in an oven.

The siloxane resins employed can be cured in deep section. These resinsare soluble in toluene and have a degree of substitution between 0.5 and1.4 organo groups per silicon atom. The organo groups referred to arelinked to the silicon by carbon to silicon bonds, and the silicon atomsare linked by Si-O-Si structures. At least a portion, and preferably atleast 25% of the monoorganosiloxane units are alkylsiloxane units inwhich the alkyl radicals contain less than five carbon atoms each. Theremainder of the monoorganosiloxane may be phenyl or higher alkylsubstituted. Partially condensed resins of the type here involved areobtainable by the hydrolysis of the corresponding chloride or ethoxyderivatives in water, preferably in the presence of a collectingsolvent, such as toluene, in which the hydrolyzate is soluble. Thesolution of hydrolyzate in solvent may be refluxed and then washed toneutrality. Other suitable methods may be employed for the preparationof these partially condensed resins.

Suitable resins and their preparation are disclosed in greater detail inthe copending applications of E. L. Warrick, Serial No. 567,901, filedDecember 12, 1944, now abandoned and of Fenn and Rauner Serial Nos.642,438, now U. S. Patent 2,517,777; 642,439, now abandoned, and642,440, now abandoned; all filed on January 21, 1946.

Resins of this type are generally best handled in solution, thecustomary organic solvents being suitable; such as ethyl alcohol,isopropyl alcohol, benzene, toluene and the like.

3 Claims. (cram-.37)

The molding powder likewise includes an ethanolamine generally in amountless than 5% based on the resin present. Mono-, di-, and triethanolaminehave been found to be equivalents in their action on the siloxane resinshere employed.

Y The inorganic filler which is employed may be in powder or fibrousform. Preferred fillers are inorganic fibrous materials, such as copper,asbestos, and glass fiber. Other fillers, such as crushed flint, crushedquartz, crushed glass; clays, titania, zinc oxide and the like may alsoor alternatively be employed.

In the molding powder, the resin and the ethanolamine are in impregnatedstate in the filler, forming a coating on the filler. The powder may beproduced by either simultaneously or separately impregnating the fillerwith the'resin and the ethanolamine, using either. a common solution ofthe two or separate solutions thereof.

The mixture of filler and solution is dried to remove the solvent. Ifdesired, a conventional mold lubricant may be added to the mixturepreferably before drying. The resin in the mixture is then partiallycured, which can be effected by heating. It is advantageous to grind thepartially cured mixture in order to obtain uniform results in thesubsequent molding operation.

The powder so produced may be molded either at room temperature or at anelevated temperature up to about 300 C. When the molding is done at roomtemperature, the molded product is desirably cured in an oven. This typeof operation is desirable, since the molding press is not employed for amajor portion of the time for curing of the molded products.Alternatively the molding may be effected at elevated temperature. Whenthe molding is effected in this manner partial or complete curing may beeffected in the press. It is preferred that the resin be only partiallycured when the product is removed from the press and that the resinreceive a final cure in an oven or the like.

The extent of cure effected at any stage of the processing is a functionboth of time and temperature. Precuring of the molding powder ispreferably effected in the range of to 300 C. When partial or finalcuring is effected in the molding operation, the temperature employedpreferably is above that employed in the precuring of the molding powderand below 300 C. Lower temperatures may be employed, but in this eventthe rate of curing in the mold is low. When final curing is effected asin an oven, the temperature is preferablyabove that at which thematerial has theretofore been subjected and below 300 C. A preferredoperation involves partially curing the powder at a temperature above100 0., molding at a higher temperature-thanthat during partialcuring ofthe powder, .andnihally curing in anovenat'a tem-v perature higher thanemployed during molding and below 300 C.

The incorporation of an ethanolamine in the molding powder giveshard'strongmoldedr-prod ucts without loss of resin duringm'oldinginthe"press and shortens to a substantial extent the A partial cureiof; the.resinain the curing time.

powder is obtained which does not prevented-:-

herence in molding and subsequent-curing.

The following examples are illustrative 'o'fthe product and method ofthis invention, and should" not be considered as definitive of the=scope thereof.

Example-1 A 00.4% solution of-a siloxane resin intoluene was: employed.for. the, production of molding powden The resin contained 2;.4 mol.percent of trimethyl siloxane units, 34 mol. per cent of 4 Similarproducts have been made using glass fiber instead of asbestos.Equivalent action on the resin may be obtained with monoethanolamine anddiethanolamine.

Emample 2 I .The molding powder described in Example 1 was molded in thesame molds at 1000 pounds per square inch at room temperature and curedin an oven on the same schedule as described in'Example 1. The-crucibless0 produced were slightly weaker than those of Example 1, butwere-entirely satisfactory for their intended purpose;. 1 l claime 1. Amolding powder composed of an inorganic filler, an organosiloxane resinin which the organic groups are methyl and phenyl radicals, and

' anethanolamine in amount from 0.4% to 5.0%

phenylsiloxane units and 63.4 mo1. per cent of methyljsiloxaneunitsh Thedegree of substitu tion of the resin was,-l.048-organo groups persilicon .atom and-.the. resin contained primarily cyclic structures.

, A: mixture waszpreparedqoi. the following in.- dicated materialsintheproportions by weight statedr,

60;4'%* toluene solution of above'resin' 328 10% toluene solutionoftriethanolaminerfl' 10; Toluene, 107 Asbestos -1; 200 Flint (200"mesh)100 Calcium stearate 10 To effect-thorough mixing this was-run twicethrough a-three roll milL v The mixture was then precured. for .tenminutes at 140 C. and ground.- The molding, powder so produced wasplaced in aamoldshapedifor the production of crucibles andnsubjected to1000 pounds per square inch pressure for one hour at 175 C, Thecrucibles were removed from the mold and cured in an oven:.-for;2.hoursat 140 0., for one hour at 200 C., .and. onehourrat 250 C.

REFERENCES CITED: I

The following references areofrecord in t lie file of th is patent; 7

UNITED STATES ensure Number Name Date 2,258,218 Rochow Oct.1 7,1.19412,337,523

2,389,807. McGregor et a1 2,442,212 Rochow May-25, 1948 OTHER REFERENCESJ ourn. Ind. and Eng. Chem 'Mar. 1909, pages- 156 and 158.

The Technology of Plastics and Resins, by 1).. Van :Nostrand Co.,published 1945; page 122.

1. A MOLDING POWDER COMPOSED OF AN INORGANIC FILLER, AN ORGANOSILOXANERESIN IN WHICH THE ORGANIC GROUPS ARE METHYL AND PHENYL RADICALS, AND ANETHANOLAMINE IN AMOUNT FROM 0.4% TO 5.0% BY WEIGHT OF SAID SILOXANE,SAID RESIN CONTAINING BETWEEN 0.5 AND 1.4 ORGANIC GROUPS PER SILICONATOM, AND BEING IN A PARTIALLY CONDENSED STATE, AND SAID INORGANICFILLER BEING COATED WITH THE RESIN.